The interior walls of tunnels, such as vehicular tunnels are often lined to provide improved appearance and for better lighting. The surfaces of such lined tunnels soon become contaminated by the adherence of soot and dust from the exhaust gas of passing vehicles, and the liners lose their interior functionability and require periodic cleaning. However, because it is difficult to remove the stains from the conventional interior tunnel liner material, cleaning operations are time and labor consuming, and the use of detergents produces problems of secondary pollution through the discharge of the cleaning water.